Well packer



G. P. MALY WELL PACKER Aug. 26, 1958 2 Sheets-Sheet 1 Filed April 2.1956 l Z Z 5 6. 7 d 57 a 0 SSS... u d WA 2/ 4 ///l/l 5 Mu,

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A1182 26; 1958 G. P. MALY 2,849,070

WELL PACKER Filed April 2, 1956 2 Sheets-Sheet 2 Patented Aug. 26, 1958WELL PACKER Application April 2, 1956, serial No. 515,563 15 claims.(ci. 16a- 179) This invention relates to a well packing or pluggingdevice and in particular concerns a well packer or plug in which Vthesealing element is actuated by means of pressure developed within thewell bore.

The use of packers or plugs in well bores in connection with suchoperations as cementing, repressuring, testing, etc. is well known, anda great variety of such tools has been proposed. Substantially all ofsuch devices, however, comprise one or more resilient sealing elementswhich are capable of being lowered into the well bore and thereinlaterally expanded until they meet the walls of the bore or the casingin Huid-tight relationship therewith. Such sealing elements areconventionally actuated by mechanical or hydraulic means controlled fromthe earths surface.

It is an object of the present invention to provide a well packer orplug in which the sealing element or elements are actuated by pressuredeveloped within the Well bore rather than at the earths surface.Another object is to provide a device of such character in which theactuating pressure is generated immediately adjacent each individualsealing element. A further object is to provide an improved sealingelement particularly adapted for use in well packers and plugs. Otherand related objects will be apparent from the following detaileddescription of the invention, and various advantages not specificallyreferred to herein will be apparent to those skilled in the art uponemployment of the invention in practice.

In the drawings which form a part of this specication:

Figure l is a longitudinal sectional view of a simple embodiment of theinvention illustrating the principle thereof.

Figure 2 is a longitudinal view of the device of Figure 1 after thesealing element thereof has been expanded to seal oil a portion of awell bore.

Figure 3 is a cross-sectional view of a novel sealing element which maybe used with the particular packing device of the invention or withprior art packers and plugs.

Figures 4a and 4b illustrate the operation of the sealing element ofFigure 3.

Figures 5-7 are cross-sectional views of alternative forms which theimproved sealing element may take.

Figure 8 is a longitudinal view, partially in cross section,illustrating a preferred form of packing device.

Figure 9 is an enlarged cross-sectional view illustrating in detail themeans for actuating the sealing elements of the device of Figure 8.

Figure l0 is a partial View taken along 'line A-A of Figure 9.

Referring now to Figures l and 2, in which like numerals indicate likeparts, the device there shown is a single element packer for closing oithe annulus between a well casing and a well tubing. Said packerconsists of a hollow mandrel or conduit 10 provided with screw threadsat its upper end whereby it may be attached to and made a part of thewell tubing string. Upper and lower plates 11 and 12 respectively arerigidly aflixed to conduit 10 in spaced relationship, and have outsidediameters somewhat smaller than the inside diameter of well casing 13 inwhich the device is to be employed. Sealing element 14, normally havingan outside diameter smaller than the inside diameter of casing 13 and aninside diameter considerably larger than the outside diameter of conduit10 but smaller than the outside diameter of plates 11 and 12, is heldbetween plates 11 and 12 but is movable with respect thereto so that itis free to expand radially. Sealing element 14 is constructed of aresilient expansible material which is not attacked by the well lluidsor by the tluid which is introduced into conduit 10 as described below,and may suitably be a hydrocarbonresistant synthetic rubber such asThiokol or neoprene. The annulus between sealing element 14 and conduit10 is filled with a body of liquid-swellable material in the form ofrelatively thin superimposed discs 15a, 15b and 15e separated by septums16a and 16b which are constructed of a substantially non-swellingmaterial capable of absorbing liquids, e. g., paper, cloth, etc. Theseptums are provided with a plurality of inwardly projecting lugs ortabs 17 which extend through suitable perforations in the wall ofconduit 10 and thus come in contact with any liquid contained in conduit10.

Operation of the device of Figures l and 2 is as follows: The assemblyis coupled to the well tubing by means of the screw threads on conduit10 and is lowered into the well casing to the desired level. There isthen introduced into the tubing, and thence into conduit 10, a liquidsuch as benzene, toluene, crude oil etc. which is capable of causingdiscs 15a-15e to swell. Such liquid contacts tabs 17 of septums 16a and16b which act as wicks to distribute such liquid to discs 15a-15c. Thelatter swell or expand with great force upon contact with such liquidand since they are confined by the outer wall of conduit 10 and theopposed faces of plates 11 and 12 the force of the expansion is directedradially outward against sealing element 14. The latter, being resilientand expansible and free to move with respect to plates 11 and 12, isthus forced outwardly against the inner wall of casing 13 to form auid-tight seal therewith, as particularly shown in Figure 2. wherein theswollen and expanded state of discs 15a-15e is indicated by more widelyspaced cross-hatching.

I am aware that it has been proposed to construct packing and pluggingtools in which a resilient sealing element is forced outwardly againstthe well casing by means of a fluid which is forced down the well tubingunder pressure. The present device, however, operates under an entirelydifferent principle in that the pressure which forces the sealingelement outwardly against the well casing is developed, not by a pump atthe earths surface and transmitted to the tool via a column of fluid oreven by the hydrostatic head of a column of liuid, but rather by a bodyof material undergoing swelling as a result of being contacted with aswelling liquid which is supplied under only nominal pressure. I havefound that such swelling pressures are remarkably high; for examplepressures as high as 10,000 pounds per square inch are developed whencertain types of rubber are contacted with a hydrocarbon liquid such astoluene. The device of the present invention operates on the principleof making use of such high pressures to actuate the sealing element.

The swellable material employed in the devices within the scope of theinvention is preferably rubber, although swelling clays, cellulosicmaterials, and the like may also be employed. All resilient naturalrubber and certain synthetic rubbers are swelled by hydrocarbons,natural oils, and many organic solvents. The extent of swelling in anyparticular liquid is dependent in part upon the extent to which therubber has been vulcanized, polymerized or otherwise treated. Thus,well-vulcanized rubber swells to a less extent and more slowly thancrude rubber, presumably because the vulcanized material contains agreater number of cross-linkages. Also, rubber which `has beenextensively milled swells more readily than a non-milled material, andrubber compositions which contain a high proportion of fillers swell toa lesser extent than compositions which contain only nominal amounts ofllers. By controlling these and other factors it is possible to preparenatural and synthetic rubbers which swell to almost any desired extent.In the practice of the present invention, any of such rubbers may beemployed since the maximum pressure developed upon swelling is more orless independent of the total extent to which the rubber is ultimatelycapable of swelling. The latter is of importance only insofar as itdetermines the dimensions of the device. Thus, in the device of Figure1, if the swellable discs a- 15C are made of rubber which is capable ofswelling only to the extent of the outside diameter of sealing element14 will have to be more nearly equal to the inside diameter of casing 13than if the swellable rubber is capable of swelling to an extent of,say, 500%. However, this is because in the latter instance sealingelement 14 will be expanded a greater radial distance rather thanbecause of any substantial difference in the pressure developed by thetwo rubbers. As a practical matter I prefer to employ a rubber which iscapable of swelling to an extent of at least about 200% in toluene,although it should be understood that toluene is not necessarily theonly liquid which may be employed in setting the packer; hydrocarbonssuch as crude oil, benzene, kerosine, and gasoline, carbontetrachloride, vegetable oils, tetralin, turpentine, and the like mayalso be employed.

In the device illustrated by Figures l and 2, sealing element 14 isshown as an integral ring constructed of a material which issubstantially non-swelling in the uids normally present in the wellbore. While sealing elements of such type operate satisfactorily whenthe inside wall of the well casing is substantially smooth, they aresubject to improvement for use in rough or irregular casings since ifmade stiff enough to withstand any substantial pressure differentialacross their lateral faces they are too stiff to extend aroundirregularities in the casing or to enter into crevasses with negativeangles. l have found that such improvement may be accomplished byconstructing the sealing face of the sealing element of a material whichis capable of swelling in one or more components of the well uid. Asimple embodiment of such an improved sealing element is shown in Figure3, wherein the element comprises a body ring 20 composed of a resilientexpansible material which is substantially non-swelling in well fluidsand having a relatively thin continuous sealing ring 21 composed of amaterial capable of being swelled by well uids vulcanized or otherwiseattached to its peripheral face. Preferably, sealing ring 21 is composedof a rubber composition capable of being swelled by petroleumhydrocarbons.

The manner in which the sealing element of Figure 3 operates is shown inFigure 4a and 4b. Figure 4a shows a sealing element consisting of anintegral ring 30, such as sealing clement 14 of Figure 1, as it pressesagainst the inside wall of a well casing 31. The latter is irregular,having imperfections in the form of projections 32 extending radiallyfrom its inside wall. As will be apparent, irregular projections 32decrease the effectiveness of the seal between casing 31 and the sealingelement 30 by decreasing the area of Contact between the two. Figure 4bshows a two-piece sealing element of the type illustrated by Figure 3and comprising a substantially non-swelling resilient body ring 33having a petroleum hydrocarbon-swellable sealing ring 34 attached to itsperipheral face. When the sealing ring comes in Contact with thehydrocarbon-containing well uid it swells and surrounds projections 32as shown, thereby increasing the area of contact between the sealingelement and the well casing and improving the seal.

Figure 5 illustrates an alternative form of sealing element, wherein theelement is composed of a resilient expansible body ring 40 constructedof a material which is substantially non-swelling in petroleumhydrocarbons. A groove is provided in the peripheral face 41 of ring 40,and carries between its walls a sealing ring 42 of a resilient materialwhich is readily swelled by petroleum hydrocarbons.

In Figure 6, the sealing element is shown composed of a substantiallynon-swellable body ring 50 having three grooves 51 provided in itsperipheral face and a sealing ring 52 of swellable material carried ineach of said grooves.

Figure 7 illustrates another form of sealing element, said elementcomprising a resilient substantially nonswellable body ring 60 havinggrooves 61 more or less in the shape of a V or U provided in itsperipheral face adjacent the upper and lower lateral faces, and having athird groove 62 cut into its peripheral face more or less midway betweenthe two V-shaped grooves. Groove 62 carries between its walls a sealingring 63 of resilient material which is relatively readily swelled bypetroleum hydrocarbons.

in the foregoing description of the sealing elements illustrated byFigures 5-7, said elements have been described as body rings ofsubstantially non-swelling material having one or more grooves cut intotheir peripheral faces, and sealing rings of swellable material carriedin said grooves. As will readily be apparent, equivalent devices may beconstructed of superimposed laminae, the requisite grooves beingattained by varying the diameter of the laminae. Also, it should beunderstood that while the ring which forms the main body of the sealingelement is described as being substantially non-swelling, all resilientmaterials eventually swell to some extent in petroleum hydrocarbons.Accordingly, the term substantially non-swelling is to be understood asbeing relative only and to distinguish the material i' rom that which isreferred to as capable of being readily swelled by well fluids.

Referring now to Figure 8, there is there shown a preferred form ofmulti-element packing device embodying the principle of the invention.Said device consists of a central conduit 70 which is attached to wellvtubing string 71 by means of collar 72. Upper retaining plate 73threadedly engages the outer wall of conduit 70, and intermediateretaining plates 74a74d slidably engage the outer wall of conduit 70.The latter is provided with shoulder portions 75a and 75b which engagecorresponding shoulder portions 76a and 76b on each of intermediateretaining plates 74 so that when conduit 'i0 is raised intermediateretaining plates 74 are likewise raised one at a time in sequencestarting from the top. Sealing elements 77a-77e in the form ofsubstantially non-swellable resilient rings are carried between theopposed faces of adjacent retaining plates. Each of sealing elements 77has an outside diameter substantially the same as that of the retainingplates and an inside diameter substantially larger than the outsidediameter of conduit 70. A body of swellable material 78a-78c 1'ills eachof the annular spaces between the outside wall of conduit 70 and theinner diameter of each of sealing elements 77. The entire assembly isheld together by means of lower retaining plate 79 which is affixed toconduit 70 by means of a shear pin 80. As is explained in greater detailhereinafter, each of intermediate rctaining plates 74 bears circularhollowed-out portions or cavities in its lateral faces, each of whichcavities forms a reservoir 81 for a body of liquid which is capable ofcausing swellable material 78 to swell and expand against sealingelements 77. A plurality of wicks 82 held in place by retaining washers83 communicate between each of reservoirs 81 and bodies of swellablematerial 78. A duct 84 communicates between each of reservoirs 81 andthe peripheral face of retaining plates 74, and provides a means forlling the reservoirs with liquid. vDucts 84 are normally closed by plugs85. Guiding shoe 86 threadedly engages conduit 70 somewhat below lowerretaining plate 79, and serves to guide the device within we'll casing87.

The operation of the device of Figure 8 is as follows: After lling eachof reservoirs 81 with a swelling liquid, e. g. toluene, and closingducts 84 with plugs 85, the entire assembly is lowered to the desiredlocation in well casing 87. The packer is held at this location untilthe swelling liquid passes into the bodies of swellable material 78 viawicks S2, thereby causing the swellable material to expand and forcesealing elements 77 firmly against the inside wall of well casing 87.When it is desired to remove the packer from the casing, well tubing 71is raised by operation of the rig hoist at the earths surface. Since thesealing elements frictionally engage the walls of the casing, shear pinS0 fractures, thereby permitting conduit 70 to move upwardly withrespect t0 the remainder of the assembly. Since upper retaining plate 73is rigidly aixed to conduit 70 it is likewise raised, thereby increasingthe width of the space between upper retaining plate 73 and the nextadjacent intermediate retaining plate 74a. The uppermost sealing element77a is thereby permitted to contract away from the walls of well casing87. As conduit 70 is raised further its first shoulder portion 75aengages shoulder portion 76a 0f intermediate retaining plate 74a,thereby causing the latter to rise and increase the gap betweenintermediate retaining plates 74a and 74h. Sealing member 77b is thuspermitted to contract away from the walls of the well casing. Similarly,as conduit 70 is raised still further, shoulder portion 75b engages theshoulder portion 76b of intermediate retaining plate 74b and causes itto rise, thereby allowing sealing element 77e to contract away from thewalls of the casing. The particular arrangement of cooperating shoulderportions 75 and 76 of intermediate retaining plates 74 and conduit 70thus permits only one of sealing elements 77 to contract away from thewall of the well casing at any one time, and the force thus required toremove the device from the well is minimized. If desired, other means ofdisengaging the assembly may be employed, e. g. the conventional J-slotarrangement or a shear pin which is broken by positive action such as aweight dropped down the well.

Referring now to Figures 9 and l0, in which like numerals indicate likeparts, which represent a fragmentary cross-sectional view of one ofintermediate retaining plates 74 of Figure 8. Said plate takes the formof a rigid metallic disc 74 having a central longitudinal opening, theupper portion of which opening has a diameter corresponding closely tothat of central conduit 70 and the lower portionof which has a diametercorresponding closely to that of shoulder portion 75 of conduit 70.Circular cavities 81a and 81b milled in the lateral faces of disc 74form reservoirs into which a body of liquid 88 can be introduced throughducts 84a and 84h communicating with the peripheral face of the disc.Duets 84a and 84b are closed by threaded plugs 85a and 85h and resilientsealing rings 89a and 8%. The lateral faces of disc 74 are milled toreceive metallic retaining washers 83a and 83b coaxially with cavitiesWicks 82a and 82h, composed of an absorbent nonswelling materal such ascotton or the like and having their exterior ends fanned out as at 90aand 90b, extend into cavities 81a and 81b through the central openingsin washers 83a and 83b, and are held therein by pins 91a and V9117. Thelatter are provided with tapered shanks which force the sides of thewicks outwardly against the walls of the openings in the retainingwashers 83a and 83b. Wicks 82a and 82h serve to conduct liquid'88 to thebodies of swellable rubber 78a and 7811 which are in Contact with thelateral faces of disc 74, whereby said bodies are caused to swell andexpand radially against resilient sealing elements 77a and 77b to forcethem outwardly against the wall of the well casing, not shown. lfdesired, an absorbent septum may be interposed between swellablematerial 78 and the exterior ends of wicks 82 to improve thedistribution of liquid 88 from Wicks 82 to swelling material 78. Sealingelements 77a and 77b are shown to be of the type illustrated by Figure3, i. e., their peripheral faces 92a and 92h are composed of a materialsuch as natural rubber which is swelled by petroleum hydrocarbons.

In order to avoid premature swelling of bodies 78a and 78h, wicks 82aand 82b are saturated with parain wax or other entity which is solublein liquid 88. The latter is likewise saturated with the wax or otherentity at a temperature which is above that at which the assembly isstored and shipped but below that of the well bore in which it is to beused. Suitably, liquid 88 is toluene saturated with paraflin at 100-140F. As will be apparent, so long as the device encounters temperaturesbelow l0O-140 F., the toluene will remain saturated with parain and willbe incapable of dissolving the parain with which the wicks are saturatedand which acts as a plug within the wicks to prevent liquid from beingconducted therethrough to swellable material 78. However, when theassembly is positioned in a well bore where it encounters temperaturesabove 100- l40 F., the toluene will no longer be saturated withparaflin, and the parafn contained in the wicks will be dissolved out ofthe same, whereby the wicks become unplugged to allow the toluene topass therethrough to swellable material 78. Thus, by constructing theassembly as described, the swelling of swellable material 78 andexpansion of sealing elements 77 against the walls of the well casingcan be controlled so as to occur only after the device has beenpositioned within the well bore.

As will be apparent to those skilled in the art, the principle of theinvention may be applied to a wide variety of packers and plugs, and thedevice of the invention may take many forms other than those illustratedand described herein. As so applied, the invention in its broadestaspects consists of a well packing or plugging device comprising anelongated body portion adapted to be lowered into a well bore, at leasttwo spaced retaining members extending from the outer surface of thebody substantially perpendicular to the lungitudinal axis thereof, aresilient substantially non-swelling sealing element in the form of aring held between adjacent retaining members adjacent the peripheriesthereof,

- a body of fluid-swellable material held between adjacent 81a and 81b.

retaining members and occupying the space between the body portion andthe sealing element, and means for directing a swelling fluid into thebody of liquid-swellable material. The invention also comprising asealing element suitable for use in contact with petroleum hydrocarbonsand essentially comprising a resilient ring-shaped member which issubstantially non-swelling in petroleum hydrocarbons and at least onebody of a resilient material capable of being swelled by petroleumhydrocarbons encircling the peripheral face of said member. Theinvention further comprises the particular means herein described fordirecting a swelling liquid into a body of liquid-swellable material.

In the appended claims, the term inert resilient ex-V pansible sealingelement is employed to define an extensible elastic sealing means whichis not substantially swelled by well uids or by the liquid which iseventually employed to swell the body of swellable material. The termliquid-swellable material is employed to dene a substance whichsubstantially increases in volume upon being contacted with a suitableliquid but does not substantially dissolve therein.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the element ormeans explained provided the apparatus stated by any of the followingclaims, or the equivalent of such stated apparatus, be constructed oremployed.

I, therefore, particularly point out and distinctly claim as myinvention:

1. A well tool comprising an elongated body portion adapted to belowered into a well bore; at least two rigid imperforate retainingplates coaxially positioned along said body portion in substantiallyparallel spaced relationship, each of the opposed faces of adjacentretaining members extending over a substantial portion of thecross-sectional area of said well bore; a ring-shaped inert resilientexpansible sealing element extending between the opposed faces ofadjacent retaining plates adjacent the peripheries thereof andsurrounding said body portion at a distance therefrom; at least onesealing ring composed of a resilient material capable of being swelledby petroleum hydrocarbons encircling the peripheral face of said sealingelement; a body of a liquid-swellable material positioned between theopposed faces of adjacent retaining plates and extending between saidbody portion and said sealing element; and means for directing aswelling liquid into intimate contact with said body of liquid-swellablematerial.

2. A well tool in accordance with claim l wherein the saidliquid-swellable material is a rubber composition capable of swelling toan extent of at least about 200 percent in toluene.

3. A well tool in accordance with claim l wherein the said sealing ringis composed of a rubber composition capable of being swelled bypetroleum hydrocarbons.

4. A well tool comprising a hollow elongated conduit capable of beinglowered into a well bore on a well tubing string; at least twosubstantially circular rigid imperforate retaining plates coaxiallypositioned along the length of said conduit in substantially parallelspaced relationship, said retaining plates having a diameter somewhatsmaller than that of the bore in which the tool is used; a ring-shapedinert resilient expansible sealing element extending between the opposedfaces of adjacent retaining plates adjacent the peripheries thereof andsurrounding said conduit at a distance therefrom; at least one'sealingring composed of a material capable of being swelled by petroleumhydrocarbons encircling the peripheral face of said sealing element; abody of petroleum hydrocarbon-swellable material positioned betweenopposed faces of adjacent retaining plates and between said conduit andsaid sealing element; and a body of a substantially non-swellingliquid-absorbing material interposed within said body of petroleumhydrocarbonswellable material and communicating with the interior ofsaid conduit.

5. A well tool in accordance with claim 4 wherein the said body ofpetroleum hydrocarbon-swellable material is a rubber composition capableof being swelled to an extent of at least about 200 percent in toluene.

6. A well tool comprising an elongated body portion adapted to belowered into a well bore; at least two substantially circular rigidimperforate retaining plates positioned along the length of said bodyportion in substantially parallel spaced relationship, each of saidretaining plates having a diameter smaller than that of the bore inwhich the tool is used and at least one of said retaining plates havinga cavity in the lateral face opposing the adjacent retaining plate;means for closing the opening of said cavity in the lateral face of saidretaining plate; means for introducing a liquid into said cavity; aring-shaped inert resilient expansible sealing element extending betweenthe opposed faces of adjacent retaining plates adjacent the peripheriesthereof; a body of liquid-swellable material positioned between theopposed faces of adjacent retaining plates and between said body portionand said sealing element; and absorbent nonswelling wick means extendingfrom within said cavity through said closing means to said body ofliquid-swellable material.

7. A well tool in accordance with claim 6 wherein the said cavity takesthe form of a circular groove in the face of said retaining plates andsaid means for introducing liquid into said cavity comprises a radialduct extending from said cavity to a removable closure at the peripheryof said retaining plates.

8. A well tool in accordance with claim 6 wherein the said body ofliquid-swellable material is a rubber composition capable of beingswelled to an extent of at least about 200% in toluene.

9. A well tool in accordance with claim 6 wherein said means forintroducing liquid into said cavity comprises at least one radial ductextending from said cavity to a removable closure at the periphery ofsaid retaining plate.

l0. A well tool comprising a hollow elongated conduit capable of beinglowered into a well bore on a tubing string, the outside diameter ofsaid conduit increasing in a plurality of steps along its length to forma plurality of conduit shoulder portions; an upper substantiallycircular rigid imperforate retaining plate atlixed to said conduit atits upper end; a guide shoe aixed to said conduit at its lower end; alower substantially circular rigid imperforate retaining plate;frangible means afhxing said lower retaining plate to said conduit atits lower end adjacent to and spaced above said guide shoe; a pluralityof substantially circular parallel rigid imperforate intermediateretaining plates corresponding in number to the number of said conduitshoulder portions, each of said intermediate retaining plates having aninwardly projecting shoulder portion slidably engaging one of saidconduit shoulder portions between said upper and said lower retainingplates, each of said inwardly projecting shoulder portions being ofshorter length than the conduit shoulder portion which it slidablyengages and the lateral faces of said intermediate retaining plateshaving at least one cavity therein; means for closing the opening ofsaid cavity in said faces; means for introducing a liquid into saidcavity; a ring-shaped inert resilient expansible sealing elementextending between the opposed lateral faces of adjacent retaining platesadjacent the peripheries thereof; a body of liquid-swellable materialpositioned between the opposed faces of adjacent retaining plates andbetween said sealing element and said conduit; and absorbent nonswellingwick means extending from within said cavity through said closing meansto said body of liquid-swellable material.

1l. A well tool in accordance with claim 10 wherein the said cavitytakes the form of a circular groove cut into the face of said retainingplate and said means for introducing liquid into said cavity comprisesat least one radial duct extending from said cavity to a removableclosure at the periphery of said retaining plate.

12. A well tool in accordance with claim 10 wherein each of said sealingelements comprises an inert resilient expansible body ring, and asealing ring composed of a material capable of being swelled bypetroleum hydrocarbons encircling the peripheral face of said body ring.

13. A sealing element for well packers and plugs comprising aring-shaped body portion composed of an inert resilient expansiblematerial, and a sealing ring composed of a material capable of beingswelled by petroleum hydrocarbons encircling the peripheral face of saidbody portion.

14. A sealing element for well packers and plugs comprising aring-shaped body portion composed of an inert resilient expansiblematerial having grooves in its peripheral face adjacent the upper andlower edges thereof, the walls of said grooves tapering inwardly fromsaid edges; and a sealing ring composed of a material capable of be- 10References Cited in the le of this patent UNITED STATES PATENTS 672,255Boberg Apr. 16, 1901 5 2,401,539 Benson June 4, 1946 2,438,673 McMahonMar. 30, 1948

